ObjectiveTo systematically review the effectiveness and safety of demethylation agents in patients with myelodysplastic syndrome. MethodsRandomized controlled trials (RCTs) about demethylation agents in treating myelodysplastic syndrome was electronically searched in PubMed, EMbase, The Cochrane Library (Issue 3, 2013), Web of Science, CNKI, VIP, WanFang Data and CBM from inception to March 2013. Two reviewers independently screened literature according to the inclusion and exclusion criteria, extracted data, and assessed methodological quality of the included studies. Meta-analysis was performed using RevMan 5.1 software. ResultsA total of 4 studies involving 816 patients were finally included. The results of meta-analysis showed that:for patients with myelodysplastic syndrome at middle/advanced stage, compared with the best supportive treatment plan, demethylation agents improved complete remission (CR) (OR=19.14, 95%CI 5.33 to 68.7, P < 0.000 01), partial remission (PR) (OR=20.63, 95%CI 5.76 to 73.93, P < 0.000 01), hematological improvement (HI) (OR=3.58, 95%CI 2.40 to 5.34, P < 0.000 01), and the incidences of Grade Ⅲ or Ⅳ neutropenia (OR=3.82, 95%CI 2.67 to 5.47, P < 0.000 01), Grade Ⅲ or Ⅳ thrombocytopenia (OR=3.98, 95%CI 2.55 to 6.23, P < 0.000 01), and mortalities (OR=0.52, 95%CI 0.35 to 0.77, P < 0.000 01), all with significant differences; and part of patients suffered from Grade Ⅲ or Ⅳ thrombocytopenia and tolerable adverse reaction caused by non-hematologic change. ConclusionCurrent evidence suggests that demethylation agents in treating myelodysplastic syndrome have apparently curative effects. Besides, it could prolong the time of turning into acute myelocytic leukemia, reduce mortalities, and improve patients' quality of life.